rechargeable energizers

[U_U]

hi, i have 6 D cell NiMH Energizer rechargeables (1.2V & 2200 mah)for my 6D maglite. i fully charged them and the light was very bright in the beginning. i put the light away for one week and then i tried turning it on again and it is very dim. any ideas why it is so dim after one week??

 

[shiftd]

self discharge? /ubbthreads/images/graemlins/icon3.gif
Nimh is not good at keeping its charge around

 

[gwbaltzell]

While NiMh have a higher self-discharge than NiCd one week to very dim does not sound normal. Recharge the cells, remove from the charger and let stand 24 hrs. Meter the voltage on each cell. Should be about 1.42 V. I think you'll find at least one that is much lower. Make sure you are using a charger made for NiMh not NiCd. NiMh are also less tolerant of reverse charging than NiCd, so turn the flashlight off as soon as there is any significant dimming. Final voltage on the weakest cell should be no less than 0.8 V (1.0 V is normally considered full discharge). And you can do alot better than Energizer for rechargeables. Likely you can find D cells with twice the capacity for half the price. However, do not mix cells of different capacities in a single flashlight.

BTW - Energizer's rated self discharge appears to be 20% in 10 days at normal room temperature. (80% charge retention).

PS. Struck me after I posted all the above that I assummed you had changed the bulb to one designed for a 5 D light. Have you?

 

[Mark_Paulus]

How new are these cells? NiMH need some initial conditioning before they reach optimal performance. So, your first 2-3 charges, you might see symptoms like you talked about. They look like they charge all the way up, but they seem to run down quickly. Charge them up and run them down a few times, and they will perform much better.

 

[Techmedic]

I will second Mark's comments - cycle them a few times to get them 'waked up. Common thing with Nicad's/Nimh's.

May need to change the bulb to go with the next cell count down to get the nice white output.

 

[U_U]

thanks for all replies. gwbaltzell, i'm using the bulb that came with the light. by the way, where do i get those really high capacity D cells? i bought my rechargeables at Londdon Drugs in Canada. any stores in canada that sell the high capacity ones?

 

[gwbaltzell]

One of the sponsors BatteryStation looks to be selling button top (the kind you want) 9000 mAh D cells for $9.50 US each. There have been recent discussions of sources and capacity of Ds.
The reason for changing the bulb is brightness. The one that came with was for alkalines 1.5 V * 6 = 9 V. Nominal voltage for nickel based rechargeables is 1.25 V * 6 = 7.5 V. This is the same as 5 alkalines. But the rechargeables maintain the voltage much longer, were to use akalines to get the full rated power out they have to be drained to 0.8 V. The rechargeables only need to be drained to 1.0 V.
There may be nothing wrong with the cells you have. Fresh from the charger the voltage may be 1.45 V or higher but in use quickly drops to 1.25 V but stays close to this level for a long time. Half discharged is 1.15 V.
Voltages in table form:
Ni -- Alky
1.42 1.55 No load
1.25 1.5 Full capacity
1.15 1.2 Half capacity
1.00 0.8 End of cycle

 

[theepdinker]

Another option you may like.
Sleeve 7 C batteries inside a 13" length of 1" pvc water pipe. Don't change the bulb. The seventh cell will make it brighter. C nimh's are available in 4500ah on line for 4 or 5 dollars US. Half the price of D high capacity and brighter than the 5 cell bulb option. That's what I do.
Theepdinker

 

[3rd_shift]

[ QUOTE ]
U_U said:
thanks for all replies. gwbaltzell, i'm using the bulb that came with the light. by the way, where do i get those really high capacity D cells? i bought my rechargeables at Londdon Drugs in Canada. any stores in canada that sell the high capacity ones?

[/ QUOTE ]

www.batterystation.com is one.
www.amondotech.com is another one.

 

[jayflash]

The info I've gotten on NiMH is that their self-discharge rate is LESS than NiCd's. My NiMH cells are older and only 1200mAh but they out last newer NiCd's for shelf life. Is it the high capacity NiMH that have a higher self-discharge rate? Thanks for any feedback.